<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        p, h3 {
            color: blue;
        } 
        .para,.heading {
            font-size: 20px;
            color: red;
            }
    </style>
</head>
<body>
    <p class="para">This is a paragraph.</p>
    <h3 class="heading">This is a heading.</h3>
</body>
</html>